Use:

Private Declare Function ReleaseCapture Lib "user32" () As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long


And then in the Mouse_Down event of the Frame:

ReleaseCapture
SendMessage Frame1.hWnd, &H112, &HF012&, 0